1. Field of the Invention
The present invention relates to a ground fault detecting device, a current collecting box using the ground fault detecting device, and a photovoltaic power generating device using the current collecting box. Particularly, the invention relates to a photovoltaic power generating device comprising a photovoltaic string including a plurality of photovoltaic modules, and a ground fault detection in the photovoltaic power generating device.
2. Description of the Prior Art
A photovoltaic cell generates direct current power by converting the natural energy into electrical energy. With increasing awareness of the recent environmental issues, a photovoltaic power generating device has received attention as a clean power generating device emitting no carbon dioxide, which contributes to the global warming.
A large scale photovoltaic power generation system of current interest, such as a mega solar system, aims at achieving an output of more than 1000 kW and includes thousands of photovoltaic modules having an output on the order of 200 W and interconnected to form arrays.
By the way, the above-described photovoltaic power generation system may sometimes encounter ground fault resulting from the deterioration of insulation performance of the photovoltaic modules, wirings or the like, which is induced by some factors including installation environment, use situation and the like. In the event of a ground fault, it is necessary to locate a poor insulation and implement an appropriate recovery process.
U.S. Pat. No. 6,593,520 discloses a photovoltaic power generating device arranged such that in the event of a ground fault in a part of a photovoltaic array, the operation of the whole photovoltaic power generating device is not suspended but only a photovoltaic string suffering the failure is disconnected from the photovoltaic power generating device.
In the above-mentioned patent document, this photovoltaic power generating device includes the current collecting box for collecting the outputs from a plurality of photovoltaic strings each including a plurality of photovoltaic panels connected in series. The current collecting box includes: a detector for outputting a failure detection signal upon detection of a failure in any one of the plural photovoltaic strings; an intermediate switch provided midway along the photovoltaic strings and shifted to an open state by the failure detection signal from the detector; and string switches capable of disconnecting for every photovoltaic strings. The current collecting box is configured such that the string switch is also switched off by the failure detection signal.
This photovoltaic power generating device is for domestic use and hence, the current collecting box is installed inside the house so that an inspection operation is relatively easy.